Mercury Montego Dome Light Bulb Size

The Mercury Montego dome light requires bulb sizes 578, 211-2, 561, 105, or 1003 depending on the specific vehicle configuration. Available data covers a range from 1968 through 2007.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2005-2007	578
1976	211-2
1975	561
1973-1974	211-2
1972	561
1970-1971	105
1968-1969	1003

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, 41mm length, end-cap contacts. 12V, 12W.	578
ANSI standard (US & Canada). Festoon bulb, 41mm length, SV8.5 base. 12V, 12W.	211-2
ANSI standard (US & Canada). Festoon bulb, 44mm length, end-cap contacts. 12V, 12W.	561
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 13W.	105
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1003

Other Locations

Additional Notes

The Mercury Montego dome light specifications span two distinct production periods: the original 1968-1976 generation and the revived 2005-2007 generation.
The 578 bulb is a festoon-type lamp rated at 12V and 12W, using end-cap contacts and measuring 41mm in length. It serves as the dome light bulb for the Mercury Montego across the 2005-2007 model years.
The 211-2 bulb shares the same 41mm festoon format and 12V/12W rating as the 578, but uses an SV8.5 base rather than end-cap contacts. This base difference makes the two bulbs non-interchangeable despite their otherwise similar specifications.
The 578 and 211-2 are physically close in size but differ in contact type, which means fitment is socket-dependent and one cannot substitute for the other without a socket mismatch.
The 561 bulb is also a festoon lamp rated at 12V and 12W with end-cap contacts, but its 44mm length distinguishes it from the 578. The 3mm difference in length means the 578 and 561 are not interchangeable.
The 105 bulb departs from the festoon format entirely, using a BA15s bayonet base and a single-filament construction rated at 12V and 13W. It is noted as a variant of the 1156 bulb family.
The 1003 bulb also uses a BA15s bayonet base and single-filament design, but is rated at a notably higher 21W compared to the 105. Despite sharing the same base type, the wattage difference between the 105 and 1003 means they serve different load requirements.
All five bulb types listed across the Montego specifications conform to ANSI standards applicable in both the United States and Canada.
The Mercury Montego (1968-1969) used the 1003 bulb, which at 21W represents the highest wattage dome light bulb across all model years in these specifications.
The BA15s bayonet base, shared by both the 105 and 1003 bulbs, is a single-contact bayonet fitting. While the base is physically compatible between the two, the difference in wattage ratings means substitution between them may not be appropriate for all applications.